Former Singapore Prime Minister Lee Kuan Yew has died early Monday. He was 91 years old. Lee was Singapore’s leader from 1959 until 1990, but remained a highly influential figure and a strategist on the city state’s economy.

Lee was hospitalized in Singapore General Hospital in early February with severe pneumonia, and was later placed on life support.

U.S. President Obama offered deepest condolences to Lee’s family. In a White House statement, Obama described Lee as a "visionary" who built "one of the most prosperous countries in the world today." Obama said Lee was "a true giant of history who will be remembered for generations to come as the father of modern Singapore and as one the great strategists of Asian affairs." The president said he joined Singaporeans in mourning Lee's death.

A survivor of the Japanese Imperial Army’s occupation of Singapore, Lee studied economics in London after the war and attended Cambridge University, gaining a law degree.

His political life began in 1954 with the formation the People’s Action Party (PAP), a coalition of middle class and pro-communist trade unionists. In 1955 Lee was the opposition leader in the legislature. But splits within the PAP with the party’s left wing led to arrests of pro-communists in 1957.

The PAP won an electoral landslide in1959, and Lee Kuan Yew became Singapore’s first Prime Minister, a position he held until 1990 before taking a post of senior minister.

Carl Thayer, a political scientist at the University of New South Wales in Australia, says Lee was pivotal to Singapore’s long term future.

“The story of modern day Singapore can’t be told without reference to Lee Kwan Yew," said Thayer. "He took the country from colonial rule to independence. He fended off challenges from the socialist left and then he dominated politics.”

Lee faced political challeges as prime minister. An early goal was the formation of a Federation of Malaysia bringing together Singapore, Malaya, Sabah and Sarawak.

But differences soon emerged between Peninsular Malaysia’s Prime Minister Tunku Abdul Rahman and Lee, especially after race riots between Chinese and Muslims in 1964 and again in 1965. And on August 9, 1965 Abdul Rahman called for separation.

“There have been differences between the central government and the leader of the Singapore state government," said Abdul Rahman. " And these differences take so many forms and are so many kinds that it has not been possible to resolve them and so we decided we must part company.”

“You see the whole of my adult life I believed in the Malaysia merger and the unity of these two territories. You know some connection by geography and ties of kinship……would you mind if we stopped for a while,” he said.

At the age of 42 Lee became Singapore’s sole leader, driving hard on economic growth to build the Republic and to foster unity. “I am not here to play someone else’s game. I have a few million people’s lives to account for and Singapore will survive.”

Foreign investment followed. With economic growth running often at near 10 percent over the decades, Lee helped define a model of capitalist development that was also adopted by the so-called “Asian Tigers:” Hong Kong, Taiwan and South Korea.

As the country industrialized, Singapore rose as a modern city state, says Michael Barr, a political scientist at Flinders University in South Australia.

“One of Lee Kuan Yew’s great achievements - I think - his positive legacies - is how he recognized and built on Singapore’s natural advantages - and capitalized on them in a way that really is exceptional,” said Barr.

Singapore became the world’s busiest seaport, only recently eclipsed by Shanghai. Investment flowed into oil refining, development as a regional transport hub; a national airline to reach global prominence and a banking sector as a vital part in global financial markets.

“He brought serious political leadership and political mass to what was a group of strong-minded and imaginative men and competent administrators. And without his political leadership would not have been able to establish the political hegemony that they have been able to,” said Barr.

Lee’s tough approach to politics and opponents also led to a reputation of “authoritarianism.” The government’s application of the Internal Security Act (ISA) against opponents and critics was used to detain politicians, activists, trade unionists.

In 1963, 100 people were arrested, including former newspaper editor Said Zahari, who was held for 17 years without trial. In 1987, 22 Roman Catholic Church officials, social activists and professionals were detained, accused of a left wing conspiracy. In the face of local and foreign media criticism Lee sued the outlets in the courts. But Lee was no apologist for his tough stance.

“Whoever governs Singapore must have that iron in him or give it up. This is not a game of cards. This is your life and mine," he said. "I’ve spent a whole life in building this and as long as I am in charge nobody’s going to knock it down.”

Singapore remains a country where the state exercises tight controls over speech. In 2014, Reporters without Borders’ Press Freedom Survey, ranked Singapore among the lowest countries in southeast Asia for press freedoms, behind Myanmar, Cambodia, Thailand and Indonesia.